Congenital absence of the internal carotid artery (ICA) is a rare anomaly and aplasia/hypoplasia of the ICA associated with other congenital malformations is uncommon, too. We report a very rare case of hypoplastic carotid canal due to hypoplastic ICA at cervical portion associated with neurofibromatosis type I (NF I). A 22-year-old male with NF I was admitted to our hospital for transient weakness of the left upper and lower limbs. Computed tomography (CT) of the brain demonstrated no abnormal findings. But bone target CT and three dimensional computed tomography (3 D-CT) showed a hypoplasia of right carotid canal. Cerebral angiography revealed that the right ICA was hypoplastic at its cervical portion and occluded at the carotid canal. Rest single photon emission computed tomography (SPECT) demonstrated normal cerebral perfusion, and SPECT with acetazolamide demonstrated showed cerebral perfusion reserve of both hemispheres, too. So he was treated conservatively at the present time. Careful follow up should be performed for such patients, because they are very rare cases and the natural history of them is unknown, too.